Process for extinguishing burning magnesium and other combustible metals



PROCESS FOR EXTINGUISHING BURNING MAG- NESIUM AND OTHER CBMBUSTIBLE -METALS Roy T. McCutchan, San Antonio, Tex., assignor to Southwest Research Institute, San Antonio, Tex.

No Drawing. Application April 28, 1955 Serial No. 504,675

19 Claims. (Cl. 252--2) This invention relates to improved processes and compositions of matter for use on fires of magnesium and other combustible metals and more particularly to the use of certain liquid extinguishing agents for quenching fires of magnesium and other combustible metals.

Magnesium fires cannot be extinguished by the common fire extinguishing agents such as water, CO foam and carbon tetrachloride. Prior to my discovery a great deal of eifort had been expended in the study of difierent materials to extinguish magnesium fires. These attempts have been only partially successful and most of the materials used for this purpose have not been suitable for the type of fires resulting from aircraft crashes.

The known methods for'extinguishing magnesium fires prior to my discovery, except for the use of a few oil'- base liquid extinguishing compositions satisfactory only for small magnesium fires, generally employed powdered materials. The more effective of the powdered materials include sand, salt, graphite, clean cast iron borings, Portland cement, powdered limestone, talc, powdered slate and shale, brass turnings, shredded asbestos, ashes, slag, dry sifted earth, crushed bituminous coal, crushed anthracite, crushed petroleum coke, calcin'ed'fullers earth, carbon black, primary and secondary ammonium phosphate, feldspar, magnesium oxide, and muscovite. Graphite is particularly ellective when thoroughly mixed with the burning magnesium, but much less so when merely used as a blanket. Materials which melt and flow over the surface of the burning'magnesium enough to 'form a completely airtight seal are also effective and include volcanic ash, potash feldspars, powdered vitrescible minerals and alkali aluminum silicate. None of these materials are suitable for application from commercial fire fighting equipment or, in general, for use on aircraft fires and other large-scale fires. Another serious limita tion in the use of such materials arisesfrom the awkward handling problem which makes them difiicult to apply to the surface of the burning metal when the fires are too large to be approached by fire fighters.

Accordingly, it is a primary object of this invention to provide an improved process for extinguishing magnesium fires and the like by the use of extinguishing agents of a form that will enable them to be made available quickly at the site of large magnesium fires, particularly at the site of an aircraft crash. Another object is to provide sucha process for the use of extinguishing agents which are adaptable for storage in and application from existing types of fire-fighting equipment and, at the same time, which will provide sufiicient cooling, quenching, or inhibiting effect on magnesium fires and the like to secure extinguishmentin the shortest possible time. A further object of my invention is to provide a process for extinguishing magnesium metal fires 'and the like by the use of extinguishing agents which are compatible with other agents commonly used to extinguish non-metallic fires.- A still further object of 2,880,172 Patented Mar. 31, 1959 my invention is to provide for the use of extinguishing agents which are available in quantity at reasonable cost and free of corrosive, irritant and toxic properties. Other objects as well as advantages of my invention will appear in the following specification and amended claims.

In accordance with my invention I have found that a solution of boric acid in certain polyhydric alcohols is highly elfective in extinguishing magnesium fires and the like. By the term polyhydric alcohol I mean a compound with a plurality of hydroxyl radicals including, by way of example, dihydric alcohols, trihydric alcohols, glycols and mono and diether derivatives of glycols. Such compositions have been found particularly adapted to extinguishing large magnesium .fires under conditions which duplicate those of an aircraft crash .fire, in which burning gasoline and magnesium must be fought simultaneously. Under such conditions, I have applied CO or conventional foam to the gasoline fire before application of my magnesium fire extinguishing agents and I have found that these extinguishing compositions may be so employed without harmful effects on the foam blankets and, conversely, the foam blankets do not impair the efiiciency of my compositions in extinguishing the magnesium fires. In general, I have found that polyhydric alcohols are suitable, economical solvents for boric acid and that the resulting solutions are compatible with water and foam extinguishing agents which may be used to extinguish other fires in the vicinity of the burning metal. In order to handle these solutions in conventional fire fighting equipmentit is desirable that the solvents employed'be liquid and of low enough viscosity to be readily pumped throughout the range of temperatures which may be anticipated for a given storage area.

In accordance with these principles, the solutions set forth in the followingexamples are illustrative of extinguishing agents which may be used in the practice of my invention:

Example 1 An extinguishing composition comprising a substantially saturated'isolution of boric acid in a liquid dihydric or trihydric alcohol having 4 through 10 carbon atoms as, for example, Z-methyl pentanediol-2,4; hexanetriol- 1,2,6; 2-ethyl hexanediol-1,3 and mixtures of these solvents. .M-ixture's of liquid dihydric and trihydric alcohols may also be employed provided the viscosity of the resulting mixture is .sufiiciently low to permit the solution to be pumped.

Example 2 An extinguishing composition comprising a solution containing 10 to 20 parts by weight of boric acid dissolved in glycols of the formula HOCH (CH OCH ,,CH OH in which the letter n represents an integer which may be varied from 1 to 3. Also a mixture of liquid glycols of this formula may be used as a solvent in which event the value of n for the component glycols appearing in appreciable quantities in the mixture may include values of l to 12, provided the average molecular weight of the resulting mixture be maintained below 315. Examples of these solvents which may be used in accordance with my invention include diethylene glycol, triethylene glycol, tetraethylene glycol, and mixtures thereof.

Example 3 An extinguishing composition comprising a substantially saturated solution of boric acid dissolved in a glycol of the formula HOCH (CHCH OCH CHCHgOH wherein n represents an integer from 1 to 3. Examples of solvents of this type include dipropylene glycol, tripropylene glycol, tetrapropylene glycol and mixtures thereof. Where mixtures of glycols of this general formula are used the value of n may bevaried from 1 to 12 for each of the principle constituents of the solvent mixture appearing in appreciable quantities, provided the average molecular weight of the entire solvent mixture does not exceed 450.

Example 4 An extinguishing composition comprising a substantially saturated solution of boric acid dissolved in ether derivatives of glycols. Said ether derivatives have the general formula R-O(C H O),, wherein R represents an alkyl radical, R represents an alkyl radical or H, and n represents an integer with a value such that the total number of carbon atoms in the compound, including those in those alkyl radicals, is from 4 to 16. Examples of solvents which may be used in accordance with this general formula include diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dibutyl ether and mixtures thereof.

Commercial mixtures of solvents containing polyhydric alcohols from two or more of the above classes of compounds are also within the teachings of my inventiun provided they otherwise conform to the requirements of viscosity. Also, it should be understood that the above examples of compositions are illustrative of preferred embodiments of my invention and other compositions may be used. Particularly, where I have designated substantially saturated solutions, other solutions containing less than a saturated solution may be employed within the teachings of my invention. Furthermore, although saturated solutions may always be employed provided pumping equipment is available to handle them, if the higher homologs the solvents enumerated above are used, the solutions tend to become very viscous and hard to pump with increased percentages of boric acid. Hence the amount of boric acid dissolved may have to be limited for some specific applications of compositions within the scope of my invention in order to obtain a solution which may be pumped by the equipment available.

Even when substantial amounts of boric acid are dissolved in these polyhydric alcohols, the resulting solutions are, to some extent at least, inflammable when subjected to the high temperatures of magnesium fires resulting in secondary fires. Therefore, it is preferable that the solvent employed should have relatively low volatility to reduce the intensity of such secondary fires. However, this inflammable quality does not preclude the use of any of the compounds shown in the above examples, since it has been found that the degree of infiammability of these distinguishing compositions does not have any significant effect upon the efficiency of the agent in its function of extinguishing magnesium fires and the like. Any secondary fire arising from ignition of my extinguishing solutions may be readily extinguished by C foam, steam or water fog after the metallic fire is extinguished.

My extinguishing solutions are adapted for use i conventional fire-fighting equipment in like manner to the use of water and chemical extinguishing agents. I prefer to pump a solid stream or heavy spray of liquid directly on the burning metal, and, when this procedure is used, I have found that the fire is extinguished as soon as the solution reaches thev burning metal surfaces. In extinguishing large fires care must be taken to dig out and extinguish burning magnesium from the center of the pile or to flow a sufficient quantity of the extinguishing agent over the surface of the burning mass to make sure the liquid covers the metal in the interior.

As an illustration of the method of extinguishing magnesium fires and the like in accordance with my invenacid and 100 parts by weight of triethylene glycol was made in accordance with the compositions described in Example 2 above, by heating the glycol to about 90 centrigrade and stirring in the boric acid. Although heat is not necessary, the boric acid dissolves more readily at this temperature than at room temperature. The extinguishing solution prepared in this manner was employed to extinguish a test fire of 115 pounds of scrap magnesium consisting of both castings and sheet metal which has been ignited by the use of a small quantity of gasoline. The magnesium fire was extinguished in five minutes with the application of 18 gallons of the prepared solution by pumping this solution to the surface of the burning magnesium so as to completely blanket the burning area. A secondary fire caused by the ignition of the extinguishing agent was readily extinguished by a small amount of standard water foam. After the fire was extinguished the remaining unburned magnesium weighed forty-five pounds.

Other similar procedures for the extinguishing of magnesium fires and the like in accordance with the teachings of my invention will be apparent to those skilled in the art as well as modifications of the specific compositions described herein for purposes of illustration. My invention, therefore, is not limited to the examples disclosed but extends to all methods and procedures falling within the true'spirit and scope of the appended claims.

What I claim is new and desire to secure by Letters Patent of the United States is: I

1. A method of extinguishing magnesium metal fires and fires of like combustible metals comprising applying a pumpable solution of boric acid directly to the surface of the burning magnesium, said solution com: prising a substantially saturated solution of boric acid dissolved in a solvent selected from the group consisting of liquid dihydric alcohols, liquids trihydric alcohols and mixtures thereof.

2. A method of extinguishing magnesium metal fires and fires of like combustible metals comprising applying. a pumpable solution of boric acid directly to the surface of the burning magnesium, said solution comprising a substantially saturated solution of boric acid dissolved in 2-methyl pentanediol-2,4.

3. A method of extinguishing magnesium metal fires and fires of like combustible metals comprising applying a pumpable solution of boric acid directly to the surface of the burning magnesium, said solution comprising a substantially saturated solution of boric acid dissolved in hexanetriol-1,2,6. 4. A method of extinguishing megnesium metal fires and fires of like combustible metals comprising applying a pumpable solution of boric acid directly to the surface of .the burning magnesium, said solution comprising a substantially saturated solution of boric acid dissolved in 2-ethyl hexanediol-1,3.

5. A method of extinguishing magnesium metal fires and fires of-like combustible metals comprising applying directly to the surface of the burning metal a solution consisting essentially of 10 to 20 parts by weight of boric acid with 100 parts by weight of a solvent, said solvent consisting of a mixture of glycols having the formula:

wherein n represents an integer from 1 to 12, said mix ture of glycols having an average molecular weight less than 315.

6. A method of extinguishing magnesium metal fires and fires of like combustible metals comprising applying a pumpable solution of boric acid directly to the surface of the burning magnesium, said solution comprising 10 to 20 parts by weight boric acid dissolved in parts by weight diethylene glycol.

7. A method of extinguishing magnesium metal fires 9. A method of extinguishing magnesium metal fires and fires of like combustible metals comprising applying directly to the surface of the burning metal a solution consisting essentially of a substantially saturated solution of boric acid in aglycol solvent, said solvent consisting of a mixture of glycols having the formula:

wherein n may be varied from 1 through 12, and the average molecular weight of said mixture of glycols is less than 450.

10. A method of extinguishing magnesium metal fires and fires of like combustible metals comprising applying a pumpable solution of boric acid directly to the surface of the burning magnesium, said solution comprising a substantially saturated solution of boric acid dissolved in dipropylene glycol.

11. A method of extinguishing magnesium metal fires and fires of like combustible metals comprising applying a pumpable solution of boric acid directly to the surface of the burning magnesium, said solution comprising a substantially saturated solution of boric acid dissolved in tripropylene glycol.

12. A method of extinguishing magnesium metal fires and fires of like combustible metals comprising applying a pumpable solution of boric acid directly to the surface of the burning magnesium, said solution comprising a substantially saturated solution of boric acid dissolved in tetrapropylene glycol.

13. A method of extinguishing magnesium metal fires and fires of like combustible metals comprising applying directly to the surface of the burning metal an extinguishing agent consisting essentially of a substantially saturated solution of boric acid in a glycol ether solvent, said glycol ether solvent comprising a mixture selected from the class consisting of glycol ethers of the general formula:

wherein R is selected from the class consisting of alkyl groups, R is selected from the class consisting of alkyl groups and hydrogen, and the n represents an integer, the value of said integer and the number of carbon atoms contained in R and R for each compound in said mixture being such that the total number of carbon atoms in the entire compound is from 4 to 16.

14. A method of extinguishing magnesium metal fires and fires of like combustible metals comprising applying a pumpable solution of boric acid directly to the surface of the burning magnesium, said solution comprising a substantially saturated solution of boric acid dissolved in diethylene glycol monoethyl ether.

15 A method of extinguishing magnesium metal fires and fires of like combustible metals comprising applying a pumpable solution of boric acid directly to the surface of the burning magnesium, said solution comprising a. substantially saturated solution of boric acid in diethylene glycol monobutyl ether.

16. A method of extinguishing magnesium metal fires and fires of like combustible metals comprising applying a pumpable solution of boric acid directly to the surface of the burning magnesium, said solution comprising a substantially saturated solution of boric acid dissolved in diethylene glycol dibutyl ether.

17. A method of extinguishing magnesium metal fires and fires of combustible metals comprising applying directly to the surface of the burning magnesium a pumpable solution consisting essentially of a liquid polyhydric alcohol and boric acid dissolved therein.

18. A method of extinguishing magnesium metal fires and fires of combustible metals comprising applying directly to the surface of the burning magnesium a pumpable solution consisting essentially of not less than ten parts by weight boric acid dissolved in parts by weight liquid polyhydric alcohol.

19. A method of extinguishing magnesium metal fires and fires of like combustible metals comprising applying directly to the surface of the burning magnesium a pumpable solution consisting essentially of a substantially saturated solution of boric acid dissolved in liquid polyhydric alcohol.

References Cited in the file of this patent UNITED STATES PATENTS Van Deursen May 31, 1870 Thrune Apr. 11, 1944 OTHER REFERENCES 

1. A METHOD OF EXTINGUISHING MAGNESIUM METAL FIRES AND FIRES OF LIKE COMBUSTIBEL METALS COMPRISING APPLYING A PUMPABLE SOLUTION OF BORIC ACID DIRECTLY OF THE SURFACE OF THE BURNING MAGNESIUM, SAID SOLUTION COMPRISING A SUBSTANTIALLY SATURATED SOLUTION OF BORIC ACID DISSOLVED IN A SOLVENT SELECTED FROM THE GROUP CONSISTING OF LIQUID DIHYDROC ALCOHOLS, LIQUIDS TRIHYDRIC ALCOHOLS AND MIXTURES THEREOF. 